Ron Coff is the figure of merit that is used to rate the performance of a radiofrequency (RF) switch transistor device. Ron Coff is the product of the Ron and Coff values of the transistor and is used to measure overall switch performance. It is important that both metrics be as low as possible, as both will affect the performance of the switch.
A mechanical switch's “on/off” state is determined by physically changing the switch's position. RF switches use an electrical input at the gate of the RF transistor to turn “on” or “off”. A positive voltage turns the switch on and a negative voltage turns it off. In design schematics, the “on” state is represented as a resistor and the “off” state as a capacitor.
When an RF switch is turned on, a low resistance allows more current to travel across the transistor. This metric is called Ron. Ron is inversely proportional to the width of the transistor. The wider the transistor the lower the resistance, which allows more of the current to get through.
A low capacitance will reduce signal loss by reducing capacitive coupling across the transistor when the switch is off. This metric is called Coff. Coff is directly proportional to the width of the transistor. The wider the transistor the higher the capacitance, and the more the signal loss via capacitive coupling across the transistor when the switch is off.
Ron Coff improvement by scaling channel length has reached a limit where the trade-offs involved in continuous scaling outweigh the benefits. To improve Ron-Coff beyond the channel length scaling limit, a new device architecture is required. For example, MEMS technology is promising for further switch improvement. Previous attempts have been made to improve Ron Coff by building devices on gallium arsenide (GaAs) substrates or silicon on sapphire (SOS) substrates, which are far more expensive to manufacture as compared to conventional silicon substrates. Furthermore, scaling in such materials is not as common as silicon, where most of the fabrication technologies can be leveraged from CMOS processing. In addition, use of GaAs or SOS substrates typically do not allow for inexpensive integration with CMOS processing flow for forming other devices, such as high density logic devices, high voltage EDMOS or LDMOS devices, such as for power amplifier applications.
Accordingly, it is desirable to provide integrated circuits having improved Ron Coff performance using conventional silicon substrates. In addition, it is desirable to provide methods for fabricating integrated circuits having improved Ron Coff performance. Furthermore, other desirable features and characteristics will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.